Rumen balance key to making the most of silage

19 August 2020

New parameters included in silage analyses give a much better indication of how the forage will perform in the rumen, allowing more efficient supplementation and purchased feed costs savings.

According to Dr Liz Homer, of Trouw Nutrition GB, most farmers and nutritionists do not go much further than metabolisable energy (ME) and crude protein when assessing the quality of silages.

She adds: “Significantly, these parameters do not indicate how a feed will perform in the rumen and the type of supplementary feeds which will be required to best balance the diet.

“The consequence will be diets which do not perform as expected leading to poorer production.”

Digestion

 Dr Homer explains that cows do not produce milk from silage, but from the products of digestion when feeds are fermented in the rumen or pass through to the intestines.

New parameters included on most silage analyses now better predict what these products of fer­mentation will be and Dr Homer advises farmers to ensure their nutri­tionist makes full use of them.

She advises farmers and their advisers to ration cows based on NutriOpt digestible intestinal protein (NDIP), which is the metabolisable protein available to the cow and dynamic energy (DyNE) which is the net energy available to the cow.

She explains that DyNE is the sum of all energy sources fermented in the rumen including sugars, neu­tral detergent fibre (NDF), residual organic matter and even lactic acid and protein which explains why silages with the same ME content can have different levels of DyNE.

She says attention also needs to be paid to the amount of total fermentable carbohydrates and protein and the rapidly fermentable proportions.

Finally, she says the acid load and fibre index help predict the impact of a silage on rumen function.

“Based on these parameters, it is possible for two silages with the same ME level to perform differ­ently in the rumen and consequently require different supplementary strategies,” she says.

“The table compares two silages which are both first cuts with a simi­lar dry matter and both are 11.3MJ/kgDM, so on first assessment would be expected to perform similarly.

“Although the ME is the same, the DyNE varies, primarily due to the amount of NDF and lignin.”

 Silage one is higher in crude protein and fermentable protein, but has lower total fermentable carbohydrates than silage two as a result of being lower in NDF.

Silage two has more rumen fermentable energy but less fermentable protein.

“When we look at the balance of rumen fermentable energy and protein, silage one has an excess of protein while silage two has a short­age of fermentable protein, in part due to having lower crude protein.

“This means, that despite having the same ME, they will need to be balanced differently.

Carbohydrate

 “Assuming they are correctly bal­anced and if cows are consuming 10kgDM, then the DyNE in silage one will support M+7.3 litres, while silage two would give M+8.3.

“But if incorrectly balanced, both will under-perform.”

Dr Homer says diets based on silage one would need to be sup­plemented with slowly fermented carbohydrate sources to balance the excess protein.

With silage two, the need is for supplementary feeds to supply fermentable protein to boost the supply of microbial protein.

Consequently, diets based on this silage would benefit from distillers, soya or rape.

 Table 1: Comparison of silages